The present invention relates to methods and apparatus for exchanging heat between a process fluid and a raw product.
It is conventional to employ a drum to subject a raw product to a continuous temperature-control process. This is effected by applying the raw product either upon the outer or inner face of the drum jacket, while a process fluid of higher or lower temperature, as compared with the raw product, is applied to the other face of the drum jacket at a charging station. As the raw product is moved from the charging station to a delivery station, due to the rotation of the drum jacket, it is influenced by the temperature of the process fluid, i.e., by heat transmission through the cross-section of the jacket, without directly contacting the process fluid. It is thereby possible, for example, to dry a raw product by the use of process fluid of higher temperature, or to cool, crystallize or freeze a product by a cooler process fluid.
It has been known heretofore to use for this purpose drums having a solid welded or cast drum jacket, the wall thickness of which is selected as a function of the demands placed on strength. A cooling drum of this type, which is used for making ice-cream, has been disclosed in German Patent Specification No. 940 227. The drum according to this disclosure comprises a vaporizer/condenser unit arranged inside the drum jacket. A cooling-coil line connected to the drum jacket extends along the inside thereof and contains the circulating process fluid, i.e., a cooling agent. Water applied to the outside of the drum jacket freezes thereon until it reaches a delivery station, due to the rotation of the drum, where the resulting ice is removed from the outside of the drum jacket and is crushed.
In order that the known drums are sufficiently strong, e.g., to avoid sagging, they possess a relatively large wall thicknesses which is detrimental to the heat transmission properties. In addition, drums of this type have a relatively high inherent weight. Also, the structure of a drum jacket is adapted for a specific raw product, so it cannot easily be converted to treat a different product.
From German Patent Specification No. 611 867 it has been known to provide a drum which is equipped with an exchangeable cover made from a suitable material such as rubber, rubber composition, felt, or the like. This cover, which is designed as a seamless hollow cylinder, is mounted on the drum by means of tensioning members provided on the end faces of the drum and comprising segments adapted to tension and detachably hold the cover. However, the cover must be supported on its inside by suitable segment-shaped jacket sections to prevent sagging. Thus, it is not possible in this way to provide a drum which is suited for heat transmission between its inside and its outside, and whose interior space is sealed.